1. Field of the Invention
The present invention relates generally to surgical implements for use in the lengthening of bones, and more specifically to an apparatus and method for intramedullary skeletal distraction.
2. Description of Related Art
The problem of limb-length discrepancies resulting from congenital, postinfectious, and post-traumatic disorders is one that has received the attention of many researchers. Various devices have been known in the art that can be attached to the ends of a sectioned bone and made to lengthen progressively, the lengthening causing growth of bone tissue at the site of sectioning and thus a commensurate lengthening of the bone. The devices are then removed when the desired length is achieved or they may be left in place as an internal splint.
External distractors, usually comprising pins passing through soft tissue and bone, can carry non-negligible potential risks of infection, pain, and muscle contractures. One benefit, however, is the accessibility of this type of device to manipulation extracutaneously.
Several internal apparati, designed to be placed within the medulla of a long bone, have been described. Two intramedullary devices for the fixation of bone fractures have been described by Roalstad et al. (U.S. Pat. No. 4,262,665) and Raftopoulos et al. (U.S. Pat. No. 4,453,539). Both devices include a threaded member and a cooperating screw positioned to hold the two ends of a broken bone together and permit them to unite and heal the fracture.
Intramedullary elongation devices have also been described in prior publications. Westerhoff (U.S. Pat. No. 4,157,715) teaches the use of osmotic pressure and a return-motion stop to effect a one-way telescoping of a pair of cylindrical members. Sirash (U.S. Pat. No. 4,384,373), Moore et al. (U.S. Pat. No. 4,502,160), and Kotz et al. (U.S. Pat. No. 4,892,546) all describe prostheses designed to elongate in response to an external adjustment; that is, an additional procedure must be undergone to lengthen the device, typically the rotation of a screw to telescopically elongate a pair of interconnected members such as a cylinder and a rod.
An attempt to obviate the need for directly contacting the elongation members has been made by Grammont et al. (U.S. Pat. No. 5,074,882; Trans. 37th Ann. Mtg. Orthopaedic Research Soc., Vol. 16, p. 657, 1991). As in previous prostheses, two telescoping tubes are used to stimulate progressive elongation of a limb. However, in this device no invasive procedure is necessary; rather, an internal ratchet mechanism responsive to a limb rotation of 20 degrees is incorporated. Since the ratchet mechanism utilizes intermeshing teeth, the minimum amount of rotation necessary to engage the ratchet is limited by the number of teeth that can be disposed about the bush. When the limb is manipulated in the appropriate direction, either by the patient or by another person, the internal ratchet mechanism permits a threaded screw to move linearly, translating one part of the device relative to another and thereby creating elongation of the device. When the limb is turned in the opposite direction, the screw does not advance linearly, and no longitudinal movement is permitted.